Does this extra-firm mattress sleep hot?

No, it is a genuinely cool-sleeping bed, scoring 8.6 for cooling. The open chamber of the Double Tempered coil core lets air circulate freely instead of trapping warmth like a solid foam slab, and a breathable cotton-blend cover moves heat off the surface. Peak surface temperature holds in the 29.1 to 31.9 degrees C range, cooler than typical, and the firm on-top feel keeps you from sinking into a warm hollow.